The purpose of this work is to characterize the components and the global system properties of the adrenocortical control system. Component analysis is carried out by studying the dynamic properties of selected elements such as the corticosteroid feedback elements. Data are analyzed by means of a computer model of adrenocortical function. The model is then used to quantify system, component and coupling functional characteristics, and to explore new experimental and ultimately new human therapeutic possibilities. The work has four themes: 1) experimentation on the adrenocortical system, 2) computer simulation of the system under study, 3) hypothesis testing by specific experiments performed both on animals and on computer models, and 4) use of computer simulations in the design of novel therapies.